Why do connecting lines look inaccurately placed?

This is a limitation in the drawing accuracy of Microsoft PowerPoint together with Microsoft Graph, which think-cell uses for most of its charts.
The accuracy depends on your current zoom factor, screen resolution, and also the exact coordinates of the shapes on the slide.
The same problem arises when using plain PowerPoint.
think-cell automatically optimizes the placement of graphical elements for print-outs and Slide Show view.